Configurable write options

[wpbonelli]

Mentioned in #241. The user should be able to configure IO-related options including for instance

• If we do end up consolidating G/A package flavors, which array input flavor with which to write supported packages (e.g. WEL vs WELG, EVT vs EVTA). Or if the user leaves this unspecified, we need to decide how to pick one automatically.
• Whether to use binary files (or maybe a size threshold over which to use them)
• Whether to use absolute or relative paths
• Whether to apply a multiplication factor to arrays
• Precision to write numeric scalars/arrays

Consider how to do this. imod-python has a WriteContext class. We could do something similar, maybe as a context manager and/or just make it attachable to any component, so you can configure on a per-package basis.

Moreover some IO-related info needs to persist from load time to write time, e.g. we load an array with factor, it should be rewritten at write time.

[wpbonelli]

The xr.DataArray.attrs and/or xr.Dataset.attrs dictionaries seem like a natural place to store info like this?